Manufacturers of integrated circuits are continually increasing circuit density in pursuit of faster processing speeds and lower power consumption. As the packing density of memory cells continues to increase, components such as capacitors must still maintain a certain minimum charge storage to ensure reliable operation of the memory cell. It is thus increasingly important that capacitors achieve a high stored charge per footprint or unit of chip area occupied.
Several techniques increase the total charge capacity of the cell capacitor without significantly affecting the chip area occupied by the cell. One technique is to use dielectric materials having higher dielectric constants (k). Such materials include tantalum pentoxide (Ta.sub.2 O.sub.5), barium strontium titanate (BST), strontium titanate (ST), barium titanate (BT), lead zirconium titanate (PZT), and strontium bismuth tantalate (SBT). Using such materials enables the creation of much smaller and simpler capacitor structures for a given stored charge requirement, enabling the packing density dictated by future circuit design.
Manufacturers, however, have encountered difficulties in incorporating these materials into the fabrication process because materials with higher dielectric constants often develop defects associated with oxygen vacancies (missing oxygen atoms in the crystal lattice). For example, when depositing barium strontium titanate, the barium strontium titanate can have missing oxygen atoms that may deform its crystalline structure and yield poor dielectric properties.
To reduce the oxygen vacancies, manufacturers often subject dielectric materials to re-oxidation anneals after their depositions. Conventional re-oxidation anneals typically heat the integrated circuit in an oxidizing environment. Ordinarily, such a process is highly oxidizing and can thus degrade other substances in the integrated circuit. For example, a re-oxidation anneal can degrade materials used in capacitor plates, electrodes, conductive plugs, the silicon substrate and the like. Such degradation can reduce the reliability of these electrical elements, and has been viewed as a significant obstacle to incorporating high dielectric materials into integrated circuits. Indeed, in some instances, manufacturers have added protective barrier layers to reduce the degradation thereby further increasing costs and fabrication complexity. Such protective barrier layers may exist, for example, between a bottom electrode material and a polysilicon plug.